P0451

DTC P0451 EVAPORATIVE EMISSION CONTROL SYSTEM PRESSURE SENSOR RANGE / PERFORMANCE




Contents




DTC Summary

Circuit Description







While the engine is running, if a predetermined condition (closed loop, etc.) is met, the purge VSV is opened by the ECM and stored fuel vapors in the canister are purged to the intake manifold. The ECM will change the duty cycle ratio of the purge VSV to control purge flow volume.
Purge flow volume is also determined by the intake manifold pressure. Atmospheric pressure is allowed into the canister through the vent valve to ensure that purge flow is maintained when negative pressure (vacuum) is applied to the canister.

Two monitors are run to confirm proper EVAP system operation.

Key-off monitor
This monitor checks for EVAP system leaks and pump module malfunctions. The monitor starts 5 hours ((+) 15 minutes) after the ignition switch is turned OFF. The 5 hours are required to allow enough time for the fuel to cool down. As a result, Fuel Tank Pressure (FTP) becomes stable and EVAP system monitor will be more accurate. Then, the electric vacuum pump creates negative pressure (vacuum) in the EVAP system and the pressure is measured. Finally, the ECM monitors for EVAP system leaks and pump module malfunctions based on EVAP pressure.

Purge flow monitor
















If EVAP system pressure change is less than 7.5 mmHg (1 kPa) when the engine is running and the purge VSV is turned ON (closed), the ECM determines that the purge flow is insufficient.

Wiring Diagram:

Step 1 - 2:

Step 3:

Step 4:

Step 5 - 8:

Inspection Procedure

NOTE:
- When a vehicle is brought into the workshop, leave it as is. Do not change the vehicle condition. For example, do not tighten the fuel cap.
- Do not disassemble the pump module.

Monitor Description




a. P0451: Pressure sensor noise
If the pressure sensor output fluctuates many times over 10 seconds, the ECM stops the EVAP system monitor, illuminates the MIL and sets DTC (2-trip detection logic).
b. P0451: Pressure sensor stuck
If the pressure does not vary for 10 seconds, the ECM stops the EVAP system monitor, illuminates the MIL and sets DTC (2-trip detection logic).
c. P0452: Pressure sensor low output
If the pressure sensor output is below 0.45 V, the ECM stops the EVAP system monitor, illuminates the MIL and sets DTC (1-trip detection logic). In this case, the pressure sensor or its circuit is open or shorted.
d. P0453: Pressure sensor high output
If the pressure sensor output is 4.9 V or more, the ECM stops the EVAP system monitor, illuminates the MIL and sets DTC (1-trip detection logic). In this case, the pressure sensor or its circuit is open or shorted.

OBDII Monitor Specification:

OBDII Monitor Specification